1. Field of the Invention
The present invention relates to a multiple-resolution scanner, particularly to a multiple-resolution flatbed scanner which offers at least two resolutions switchable without any mechanical movement.
2. Description of Related Art
Conventionally, text and image data of different types are read by scanners of different resolutions and with different scanning areas. For example, normal text is usually read from an A4 area with a resolution of 300 dpi. For color photographs, 4 inch and 600 dpi are regularly used values for linear size and resolution. Slides and negative films require a resolution of 1200 dpi for satisfactory results, but typically only a linear size of about one inch.
Conventional scanners aim at only one application for a certain image data type. Most scanners on the market are designed for A4 areas at a comparatively low resolution. For scanning photographs, scanners with a smaller scanned area and higher resolution are available. Any user purchasing a scanner needs to consider the intended application and decide which type of scanner is most suitable. For different applications, several scanners are needed, which is not convenient.
For overcoming the deficiency of only one application of conventional scanners, scanners offering multiple resolutions have appeared on the market. For example, Taiwan patent no. 232398 "Multiple lens switching system" discloses a multiple resolution image reading system. By switching between lenses with various focal lengths, the resolution is varied. The lenses are alternatively moved in front of a single CCD detector, so as to obtain different resolutions.
However, a conventional multiple resolution scanner requires, apart from a plurality of lenses, a mechanism for driving a mechanical movement of the lenses as well as enough space to allow the lenses to be switched back and forth. This leads to a large volume of a conventional multiple-resoution scanner.